JP2021150015A - Lithium air battery - Google Patents

Abstract

To provide a lithium air battery in which an over voltage at a time of charging and discharging is reduced.SOLUTION: A lithium air battery 20 of the present disclosure, comprises: a negative electrode 21 having a negative electrode active material absorbing and discharging a lithium; a positive electrode 22 made of a carbon material containing no binding material, and using oxygen as a positive active material; and a non-aqueous electrolyte 26 which is in contact with the positive electrode, and contains a mixed solvent of acetonitrile and dimethyl sulfoxide within a range of 25 volume% or more and 90 volume% or less. In the lithium air battery 20, the positive electrode 22 may be composed of carbon paper. Besides, the negative electrode 21 may include a solid electrolyte 25 having a lithium metal as a negative active material and conducting the lithium ion between the positive electrode 22 and the negative electrode 21.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a lithium-air battery.

Conventionally, it has been proposed to use a non-aqueous electrolytic solution containing acetonitrile in a lithium-air battery. For example, Patent Document 1 proposes to increase the discharge capacity by using acetonitrile as the solvent of the non-aqueous electrolytic solution in contact with the positive electrode. Further, for example, Non-Patent Document 1 reports that the addition of 0.1 M of dimethyl sulfoxide to an electrolytic solution containing acetonitrile improves the solubility of the _{reaction intermediate LiO 2 by an electrochemical method.} There is. Further, Non-Patent Document 2, consider the various electrolyte solvent such as acetonitrile or dimethyl sulfoxide, O ₂ ^- as solvated for ions or Li ⁺ ions is large, discharge potential i.e. O ₂ / Li ⁺ -O ₂ ^- of Experiments have shown that the standard redox potential of the redox pair drops.

Japanese Unexamined Patent Publication No. 2017-168190

Electrochem. Commun. 31 (2013) 56. Angew. Chem. Int. Ed. 55 (2016) 3129.

However, in the lithium-air battery of Patent Document 1, although the discharge capacity can be increased, the overvoltage at the time of charging / discharging may be high. Further, Non-Patent Document 1 suggests that the addition of dimethyl sulfoxide to acetonitrile may improve the capacity at the time of discharge, but the overvoltage at the time of charging / discharging has not been studied. Further, in Non-Patent Document 2, _{the standard redox potential of the redox pair of O 2} / Li ⁺ −O ₂ ⁻ related to the overvoltage at the time of discharge is examined, but the overvoltage at the time of discharge increases when dimethylsulfoxide is used. It suggests that this should be done, and the effect on overvoltage during charging has not been investigated.

The present disclosure has been made in view of such a problem, and an object of the present disclosure is to provide a lithium-air battery in which an overvoltage during charging / discharging is reduced.

As a result of diligent research to achieve the above-mentioned object, the present inventors used a self-supporting carbon material containing no binder for the positive electrode, and added dimethylsulfoxide to the electrolytic solution in an amount of 25% by volume or more and 90% by volume or less. It has been found that if a mixed solvent of acetonitrile and dimethylsulfoxide contained in the range is contained, a lithium-air battery with reduced overvoltage during charging and discharging can be obtained, and the lithium-air battery of the present disclosure has been completed.

That is, the lithium-air battery of the present disclosure is
A negative electrode with a negative electrode active material that occludes and releases lithium,
A positive electrode made of carbon material that does not contain a binder and uses oxygen as the positive electrode active material,
A non-aqueous electrolytic solution containing a mixed solvent of acetonitrile and dimethyl sulfoxide, which is in contact with the positive electrode and contains dimethyl sulfoxide in a proportion of 25% by volume or more and 90% by volume or less.
It is equipped with.

In the present disclosure, it is possible to provide a lithium-air battery in which an overvoltage during charging / discharging is reduced. The reason why such an effect is obtained is presumed as follows, for example. In the lithium-air battery of the present disclosure, the positive electrode is made of a carbon material containing no binder, and the non-aqueous electrolyte solution is defined as acetonitrile having high ^{Li +} ion conductivity and dimethyl sulfoxide that is easily solvated ^{with Li + ion.} Contains a mixed solvent containing in the proportion of. As a result, electron transfer and substance transfer between the positive electrode and the non-aqueous electrolytic solution become smooth, and electron transfer on the positive electrode surface and activation energy of ion conduction in the non-aqueous electrolytic solution are reduced, so that during charging and discharging. It is presumed that the overvoltage of the

Explanatory drawing which shows an example of the lithium-air battery 20 schematically. The graph which shows the relationship between the charge / discharge capacity and the charge / discharge potential of Experimental Examples 1-5.

The lithium-air battery of the present disclosure has a negative electrode having a negative electrode active material that occludes and releases lithium, a positive electrode made of a carbon material that does not contain a binder and has oxygen as a positive electrode active material, and a positive electrode that comes into contact with the positive electrode and contains 25 dimethylsulfoxide. A non-aqueous electrolytic solution containing a mixed solvent of acetonitrile and dimethylsulfoxide contained in a proportion of 50% by volume or more and 90% by volume or less is provided.

In this lithium-air battery, the negative electrode has a negative electrode active material that occludes and releases lithium. Examples of the negative electrode capable of occluding and releasing lithium include metallic lithium and lithium alloys, as well as metal oxides, metal sulfides, and carbonaceous substances that occlude and release lithium. Examples of the lithium alloy include alloys of aluminum, tin, magnesium, indium, calcium and the like with lithium. Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of the metal sulfide include tin sulfide and titanium sulfide. Examples of the carbonaceous substance that occludes and releases lithium include graphite, coke, mesophase pitch carbon fiber, spherical carbon, and resin calcined carbon.

In this lithium-air battery, the positive electrode uses oxygen from a gas as the positive electrode active material. The gas may be air or oxygen gas. The positive electrode is made of a carbon material that does not contain a binder. The binder is a material that holds the active material in the form of particles, and is, for example, a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), polypropylene, polyethylene, or the like. Examples thereof include rubbers such as thermoplastic resins, ethylene propylene diene monomer (EPDM) rubbers, sulfonated EPDM rubbers and natural butyl rubbers (NBR), as well as cellulose compounds and styrene butadiene rubbers (SBR). The positive electrode may contain carbon fibers having a diameter of 5 μm or more and 20 μm or less as a carbon material that does not contain a binder. The carbon material may be, for example, one capable of maintaining an independent shape only with the carbon material, or may be a sheet-like material such as carbon paper or carbon felt. When the carbon material is made of carbon fibers, the fiber directions may be oriented. The carbon material may have a small pore volume such as micropores or mesopores formed in the carbon material itself, such as 0.01 cm ³ / g or less, or may have no pores. Further, the carbon material may have properties similar to porous due to the space formed by the carbon fibers. The carbon material preferably has a gas permeability in the range of 100 (mL · mm / (cm ² · h · Pa)) or more and 300 (mL · mm / (cm ² · h · Pa)) or less. In this range, for example, a non-aqueous electrolytic solution or oxygen is easily permeated, which is preferable. When the positive electrode is formed of such a carbon material, high-power discharge can be continuously performed without the surface of the positive electrode being completely covered with the discharge product. The positive electrode may contain a lithium oxide or a lithium peroxide which is a discharge product. Further, the positive electrode may include a catalyst. As the catalyst, for example, one that oxidizes and reduces oxygen is preferable, and a metal oxide such as manganese dioxide or tricobalt tetraoxide may be used, or a metal such as Pt, Pd, or Co may be used. It may be an organic or inorganic compound such as metallic porphyrin, metallic phthalocyanine, ionized fullerene, carbon nanotubes and the like.

In this lithium-air battery, the non-aqueous electrolyte solution in contact with the positive electrode is a mixture of acetonitrile (hereinafter also referred to as AN) containing dimethyl sulfoxide in a proportion of 25% by volume or more and 90% by volume or less and dimethyl sulfoxide (hereinafter also referred to as DMSO). Contains solvent. When the mixed solvent of acetonitrile and dimethyl sulfoxide contains dimethyl sulfoxide in a proportion of 25% by volume or more and 90% by volume or less, the overvoltage during charging and discharging is reduced. The mixed solvent preferably has a large proportion of dimethyl sulfoxide from the viewpoint of further reducing the overvoltage during charging and discharging. For example, the proportion of dimethyl sulfoxide may be 40% by volume or more, or 50% by volume or more. .. Further, the mixed solvent preferably has a small proportion of dimethyl sulfoxide from the viewpoint of increasing the charge / discharge capacity. For example, the proportion of dimethyl sulfoxide may be 85% by volume or less, or 75% by volume or less. In the mixed solvent, acetonitrile is used except for dimethyl sulfoxide (the balance). In the mixed solvent, the proportion of acetonitrile may be 10% by volume or more, 15% by volume or more, or 25% by volume or more. Further, in the mixed solvent, the proportion of acetonitrile may be 75% by volume or less, 60% by volume or less, or 50% by volume or less. The non-aqueous electrolyte solution may contain a supporting salt. The supporting salt is not particularly limited, but is, for example, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₃ ), LiN (C _2). A known supporting salt such as F ₅ SO ₂ ) _{2 can be used.} These supporting salts may be used alone or in combination of two or more. The supporting salt may be contained in a proportion of 2 mol or less per liter of dimethyl sulfoxide, or may be contained in a proportion of 1 mol or less. The supporting salt may be contained in a proportion of 0.1 mol or more per liter of dimethyl sulfoxide. The concentration of the supporting salt in the non-aqueous electrolyte solution is preferably 0.1 to 2.0 M, more preferably 0.5 to 1.8 M. The non-aqueous electrolyte solution may contain components other than the above-mentioned mixed solvent and supporting salt, for example, an ionic liquid or an ether solvent. In the non-aqueous electrolyte solution, the proportion of the components other than the mixed solvent and the supporting salt is preferably small, preferably 50% by volume or less, more preferably 20% by volume or less, further preferably 10% by volume or less, and not contained. More preferred. Examples of the ionic liquid include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (DEME-TFSI), N, N-diethyl-N-ethyl-. N- (2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide, N-methyl-N-propylpiperidiumbis (trifluoromethylsulfonyl) imide, 1-methyl-3-propylimidazolium bis (trifluoromethyl) Examples thereof include sulfonyl) imide and 1-ethyl-3-butylimidazolium tetrafluoroborate. Examples of the ether solvent include chain ethers such as dimethoxyethane, triethylene glycol, and tetraethylene glycol. An ionic liquid, an ether solvent, or the like may be used alone, or a plurality of them may be mixed and used.

In this lithium-air battery, a separator may be provided between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium-air battery. The membrane is mentioned. These may be used alone or in combination of two or more.

In this lithium-air battery, a solid electrolyte that conducts lithium ions may be provided between the positive electrode and the negative electrode. In this way, a short circuit between the positive electrode and the negative electrode can be prevented. When lithium metal is used as the negative electrode active material, it is desirable to provide this solid electrolyte. Acetonitrile contained in the non-aqueous electrolyte solution may be reduced when it comes into contact with a lithium metal. In this lithium-air battery, when the negative electrode is a lithium metal, the physical contact between acetonitrile and the negative electrode can be blocked by the solid electrolyte, and deterioration of the non-aqueous electrolyte solution can be further suppressed. The solid electrolyte is preferably a dense plate-like body, and for example, the porosity is preferably 5% or less, more preferably 2% or less. Examples of the solid electrolyte include glass ceramics, Li nitrides, halides, and oxidates. Specific examples of the glass ceramics include Li _{1 + X} Ti ₂ Si _X P _3-X O ₁₂ / AlPO ₄ (OHARA electrolyte) and Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (LAGP). .. In addition, solid electrolytes introduced in JP-A-2009-12291, for example, garnet-type oxide Li _{5 + X} La ₃ (Zr _X , Nb _2-X ) O ₁₂ (X is 1.4 ≦ X < 2), garnet-type oxide Li ₇ La ₃ Zr ₂ O ₁₂ , garnet-type oxide Li ₇ ALa ₃ Nb ₂ O ₁₂ (A = Ca, Sr, Ba), and the like can also be used. As the solid _{electrolyte, Li 3.25 Ge 0.25 P 0.25 S} 4, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Examples include Li ₃ PO _{4- Li 2} S-SiS ₂ , phosphorus sulfide compounds and the like. Further, the solid electrolyte may be a perovskite-type ionic conductive oxide containing Li, Sr and Zr. The basic composition of this perovskite-type ionic conductive oxide is SrZrO _3, and Sr sites and Zr sites may be substituted with other elements.

In a lithium-air battery provided with a solid electrolyte, an ion conductive medium different from the non-aqueous electrolyte solution on the positive electrode side may be contained between the negative electrode and the solid electrolyte. The ionic conduction medium may be a non-aqueous electrolyte solution, a gel electrolyte, or the like. The ionic conduction medium may contain, for example, a protonic organic solvent. This organic solvent may be contained in, for example, 50% by volume or more, 70% by volume or more, or 80% by volume or more in the ionic conduction medium. Examples of such an organic solvent include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, chain ethers and the like. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like. Examples of the cyclic ester carbonate include gamma-butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran and the like. Examples of the chain ether include dimethoxyethane, triethylene glycol, tetraethylene glycol and the like. These may be used alone or in combination of two or more. Further, the ionic conduction medium may contain the above-mentioned ether solvent or ionic liquid. Moreover, this ion conduction medium may contain the above-mentioned supporting salt. The type and concentration of the supporting salt may be similar to that of the non-aqueous electrolyte solution on the positive electrode side. The concentration of the supporting salt may be higher than that of the non-aqueous electrolyte solution on the positive electrode side.

The shape of the lithium-air battery of the present disclosure is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Further, it may be applied to a large-sized vehicle used for an electric vehicle or the like. FIG. 1 is an explanatory diagram schematically showing an example of the lithium-air battery 20 of the present disclosure. The lithium-air battery 20 comprises a negative electrode 21 having a negative electrode active material that stores and releases lithium, a positive electrode 22 that uses oxygen as a positive electrode active material, and a solid electrolyte 25 disposed between the negative electrode 21 and the positive electrode 22. I have. There is an ionic conduction medium 24 that conducts lithium ions between the negative electrode 21 and the solid electrolyte 25, and a non-aqueous electrolyte solution 26 that conducts lithium ions between the positive electrode 22 and the solid electrolyte 25. Further, the lithium-air battery 20 includes a casing 28, a pressing member 31, and a gas reservoir 32. The casing 28 is an insulator container for accommodating the negative electrode 21 and the positive electrode 22. The pressing member 31 is a member that presses the positive electrode 22, and oxygen can flow through the inside. The gas reservoir 32 contains a gas containing oxygen (for example, dry air) in the gas reservoir 32, and supplies oxygen to the positive electrode 22 via the pressing member 31. The positive electrode 22 is made of a carbon material that does not contain a binder. Further, the non-aqueous electrolytic solution 26 contains a mixed solvent of acetonitrile and dimethyl sulfoxide containing dimethyl sulfoxide in a proportion of 25% by volume or more and 90% by volume or less.

Here, the reaction at the positive electrode of the lithium-air battery will be described. At the positive electrode (air electrode) of a lithium-air battery, it is considered that the reaction represented by the following formula (1) proceeds with charging and discharging. At the time of discharge, the formula (1) proceeds to the right side, and Li ₂ O ₂ is deposited on the surface of the positive electrode. During charging, equation (1) proceeds to the left, Li ₂ O ₂ is oxidatively decomposed, Li ⁺ ions are dissolved in the electrolytic solution, and oxygen gas is generated at the same time. The potential required for the progress of equation (1) is theoretically 2.94V (Li / Li ⁺ reference), but in an actual lithium-air battery, both charging and discharging are, for example, 0.2 to 1. The reaction does not proceed unless an overvoltage of about 5 V is applied. Therefore, the energy efficiency of the lithium-air battery (the ratio of the energy obtained at the time of discharge to the energy required at the time of charging) is low, which is one of the problems. It is considered that the reaction of the formula (1) at the time of charging proceeds through the following formulas (2) to (4).

In the lithium-air battery of the present disclosure, the positive electrode is made of a carbon material that does not contain a binder. It is considered that this improves the electron conductivity at the interface between the positive electrode and the non-aqueous electrolyte solution or at the interface between the positive electrode and Li ₂ O _2. Further, in the lithium-air battery of the present disclosure, the non-aqueous electrolyte solution contains a mixed solvent of dimethyl sulfoxide, which is easily solvated with ^{Li + ions, and acetonitrile, which has high Li +} ion conductivity, in a predetermined ratio. As a result, charge transfer and ion conduction in the non-aqueous electrolyte solution are required at the interface between the positive electrode and the non-aqueous electrolyte solution, the interface between the positive electrode and the Li ₂ O ₂ or the interface between the Li ₂ O _{2 and the non-aqueous electrolyte solution.} It is thought that energy can be reduced. As a result, in the lithium-air battery of the present disclosure, it is considered that the overvoltage at the time of charging / discharging can be reduced, and as a result, the energy efficiency can be improved.

In the present disclosure described in detail above, as described above, it is possible to provide a lithium-air battery in which an overvoltage during charging / discharging is reduced. Further, in this lithium-air battery, ^{acetonitrile having high Li +} ion conductivity and oxygen solubility is used as a mixed solvent. As a result, the charge / discharge capacity can also be set to a relatively high value. Therefore, in the present disclosure, it is possible to realize a high-capacity lithium-air battery having characteristics of high energy density and high output.

It goes without saying that the present disclosure is not limited to the above-described embodiment, and can be implemented in various embodiments as long as it belongs to the technical scope of the present disclosure.

Hereinafter, an example in which the lithium-air battery of the present disclosure is specifically manufactured will be described as an example. Experimental Examples 1 to 3 correspond to Examples, and Experimental Examples 4 to 5 correspond to Comparative Examples. It goes without saying that the present disclosure is not limited to the examples shown below, and can be carried out in various aspects as long as it belongs to the technical scope of the present disclosure.

[Experimental Example 1]
(Making a lithium-air battery)
Carbon paper (manufactured by Toray Industries, Inc., TGP-H-060) ^{was cut out to an area of 3.14 cm 2} to form a positive electrode for a lithium-air battery. This carbon paper has a gas permeability of 194 (mL · mm / (cm ² · h · Pa)) and is made of carbon fibers having a diameter of 20 μm or less. As the negative electrode, metallic lithium (manufactured by Tanaka Kikinzoku) having a diameter of 10 mm and a thickness of 0.5 mm was used. Using these, the lithium-air battery shown in FIG. 1 was produced. First, the negative electrode 21 was installed in the casing 28 made of SUS, and the lithium conductive solid electrolyte 25 (manufactured by OHARA) was installed between the negative electrode 21 and the casing 28. Between the negative electrode 21 and the solid electrolyte 25, 5 mL of a non-aqueous electrolyte solution (electrolyte solution A) was injected as an ionic conduction medium 24. As the electrolytic solution A, a solution (manufactured by Kanto Chemical Co., Inc.) containing 30 parts by mass of ethylene carbonate and 70 parts by mass of diethyl carbonate containing 1 M of lithium tetrafluorosulfonylimide (hereinafter, LiTFSI) as a supporting salt was used. Next, 0.5 M LiTFSI in a mixed solvent (AN / DMSO volume ratio = 50/50) of acetonitrile (also referred to as AN) and dimethyl sulfoxide (also referred to as DMSO) containing dimethyl sulfoxide in a proportion of 50% by volume. A non-aqueous electrolyte solution containing the above was prepared (electrolyte solution B). 200 μL of this non-aqueous electrolyte solution (electrolyte solution B) was injected between the solid electrolyte 25 and the positive electrode 22. The cell was fixed by pressing with a pressing member 31 capable of allowing air to flow from above the positive electrode 22. In this way, the lithium-air battery of Experimental Example 1 was obtained. Although not shown, the casing 28 can be separated into an upper portion that contacts the positive electrode 22 and a lower portion that contacts the negative electrode 21, and the positive electrode 22 and the negative electrode 21 are electrically insulated by the presence of an insulating resin.

(Charge / discharge test)
The lithium-air battery thus obtained is set in a charging / discharging device (model name 5V / 100MA) manufactured by Asuka Electronics, and ^{a current of 0.63 mA (200 μA / cm 2} ) is applied in the direction from the positive electrode 22 to the negative electrode 21. It was flowed and discharged until the discharge potential became 1.7 V or less. ^{Subsequently, a current of 0.063 A (20 μA / cm 2} ) was passed from the negative electrode 21 to the positive electrode 22 to charge the battery until the charging potential became 4.3 V or higher. This charge / discharge test was performed at 25 ° C.

[Experimental Example 2]
A charge / discharge test was carried out in the same manner as in Experimental Example 1 except that the mixed solvent of the electrolytic solution B was replaced with a mixed solvent having an AN / DMSO volume ratio of 25/75.

[Experimental Example 3]
A charge / discharge test was carried out in the same manner as in Experimental Example 1 except that the mixed solvent of the electrolytic solution B was replaced with a mixed solvent having an AN / DMSO volume ratio of 75/25.

[Experimental Example 4]
A charge / discharge test was carried out in the same manner as in Experimental Example 1 except that the mixed solvent of the electrolytic solution B was changed to the AN single solvent.

[Experimental Example 5]
A charge / discharge test was carried out in the same manner as in Experimental Example 1 except that the mixed solvent of the electrolytic solution B was replaced with a DMSO single solvent.

(Results and discussion)
FIG. 2 shows a graph showing changes in potential and battery capacity in the charge / discharge tests of Experimental Examples 1 to 5. Table 1 shows the volume ratio of AN / DMSO of Experimental Examples 1 to 5, the discharge potential (V) when the discharge capacity is 25 mAh / g, the charge potential (V) when the charge rate is 50%, and the discharge capacity. (MAh / g) are shown together.

As shown in FIGS. 2 and 1, in Experimental Examples 1 to 3 in which the mixed solvent of AN and DMSO was used as the electrolytic solution solvent, either Experimental Example 4 (AN single solvent) or Experimental Example 5 (DMSO single solvent) was used. Even in comparison, the discharge potential showed a high value, and it was found that the overvoltage during discharge was reduced as compared with Experimental Examples 4 and 5. Further, in Experimental Examples 1 to 3, the charging potential was lower than that of both Experimental Examples 4 and 5, and the overvoltage during charging was also reduced as compared with Experimental Examples 4 and 5. I understand. Further, in Experimental Examples 1 to 3, the charge / discharge capacity was higher than that in Experimental Example 5 in each case. From these facts, it was found that the lithium-air batteries of Experimental Examples 1 to 3 have the characteristics of high output and high energy density.

In Experimental Example 4 (AN single solvent), although the charge / discharge capacity was large, the overvoltage during charge / discharge was large. This, as the solvent of the nonaqueous electrolytic solution, was presumed to be due to using the Li ⁺ ion conductivity is high Li ⁺ solvation difficult acetonitrile against ions alone.

In Experimental Example 5 (DMSO single solvent), the overvoltage during charging and discharging was reduced as compared with Experimental Example 4. This is due to the effect of solvation due to the use of dimethyl sulfoxide alone, which is easily solvated with both _{O 2} ^- ion and Li ⁺ ion, as the solvent for the non-aqueous electrolyte solution. It was presumed that the overvoltage was reduced. However, in Experimental Example 5, the overvoltage during charging / discharging could not be reduced as much as in Experimental Examples 1 to 3. It was speculated that this is because the overvoltage rises relatively early because the conductivity of ^{Li +} ions is low in dimethyl sulfoxide.

On the other hand, in Experimental Examples 1 to 3, a ^{mixed solvent containing acetonitrile having high Li +} ion conductivity, Li ⁺ ions and dimethyl sulfoxide which is easily solvated is used as the solvent of the non-aqueous electrolyte solution. As a result, charge transfer and ion conduction in the non-aqueous electrolyte solution are required at the interface between the positive electrode and the non-aqueous electrolyte solution, the interface between the positive electrode and the Li ₂ O ₂ or the interface between the Li ₂ O _{2 and the non-aqueous electrolyte solution.} It was speculated that the energy was reduced and the overvoltage was reduced. That is, in Experimental Examples 1 to 3, both the solvation effect of dimethyl sulfoxide and the high Li ⁺ ionic conductivity of acetonitrile work to reduce charge transfer energy and substance transfer energy, and overvoltage during charging and discharge during charging. It was speculated that both overvoltages were reduced. In Experimental Examples 1 to 3, the positive electrode is made of a carbon material that does not contain a binder. It is presumed that this also improved the electron conductivity at the interface between the positive electrode and the non-aqueous electrolyte solution or the interface between the positive electrode and Li ₂ O _{2 and reduced the overvoltage during charging and discharging.}

Of Experimental Examples 1 to 3, the proportion of dimethyl sulfoxide in the mixed solvent is as small as 25% by volume, and the proportion of dimethyl sulfoxide is 50% by volume in Experimental Example 1 and the proportion of dimethyl sulfoxide is 75% by volume as compared with Experimental Example 3. In Experimental Example 2, the overvoltage was smaller both during charging and during discharging. From this, it was found that the ratio of dimethyl sulfoxide in the mixed solvent is preferably 25% by volume or more, more preferably 40% by volume or more, and further preferably 50% by volume or more. Further, since the overvoltage during charging and discharging of Experimental Examples 1 to 3 containing acetonitrile is smaller than that of Experimental Example 5 in which the ratio of dimethyl sulfoxide in the mixed solvent is 100%, acetonitrile is contained in the mixed solvent to some extent. If so, it is considered that the overvoltage can be reduced, and it is presumed that the proportion of dimethyl sulfoxide may be 90% by volume or less, 85% by volume or less, or 75% by volume or less. From the viewpoint of improving the charge / discharge capacity, it was found that the proportion of dimethyl sulfoxide is preferably 90% by volume or less, more preferably 85% by volume or less, and further preferably 75% by volume or less.

The present disclosure is available to the battery industry.

20 Lithium-air battery, 21 Negative electrode, 22 Positive electrode, 24 Ion conductive medium, 25 Solid electrolyte, 26 Non-aqueous electrolyte, 28 Casing, 31 Pressing member, 32 Gas reservoir.

Claims (6)

A negative electrode with a negative electrode active material that occludes and releases lithium,
A positive electrode made of carbon material that does not contain a binder and uses oxygen as the positive electrode active material,
A non-aqueous electrolytic solution containing a mixed solvent of acetonitrile and dimethyl sulfoxide, which is in contact with the positive electrode and contains dimethyl sulfoxide in a proportion of 25% by volume or more and 90% by volume or less.
Lithium-air battery with. The mixed solvent contains dimethyl sulfoxide in a proportion of 40% by volume or more and 85% by volume or less.
The lithium-air battery according to claim 1. The mixed solvent contains dimethyl sulfoxide in a proportion of 50% by volume or more and 75% by volume or less.
The lithium-air battery according to claim 1 or 2. The lithium-air battery according to any one of claims 1 to 3, wherein the positive electrode contains carbon fibers having a diameter of 5 μm or more and 20 μm or less as a carbon material that does not contain the binder. The lithium-air battery according to any one of claims 1 to 4, wherein the positive electrode is made of carbon paper as a carbon material containing no binder. The negative electrode has a lithium metal as the negative electrode active material.
The lithium-air battery according to any one of claims 1 to 5, further comprising a solid electrolyte that conducts lithium ions between the positive electrode and the negative electrode.

Images